What do you mean by 2 tablespoons of GAC, do you mean in a media reactor or in a bag? Sorry that's probably a stupid question, it's just that in freshwater we just add a bag of carbon. Sorry for my ignorance.As mentioned I would recommend skimmer for now and add other filtration only to address issues.
I only use skimmer and GAC (2 tablespoons per 60 gal changed every 4 weeks), I use corals as main filtration and others methods as supplement when required.
I use GAC because I have mixed reef and it helps with coral warfare.
I also carbon dose, but mainly to promote bacteria that hopefully provides another food source for corals,
For parameters pick your salt and use that as your target. See how things progress and maybe change at some point.
I like TM Pro reef salt and use it as a baseline.
BRSTV is there to sell, so take what they say with grain of salt. Likely you will not need most of the items but there is nothing wrong with experimenting.
At the start water change will be enough, once it is not (months from now) I would recommend looking into TM AFR.
You can hand dose AFR daily or you can use a doser. It is easy to use and you can pay attention to the fish, corals etc…
Good luck,